The invention relates to fluid valves and more particularly to a coolant loss valve used typically in a protective system for diesel engines and the like.
Such protective system is shown, for example, in U.S. Pat. No. 3,877,455. Here, fuel is supplied to a master valve and then routed to an engine so long as certain conditions are met. Among these conditions are sufficient oil pressure, coolant pressure and a lack of excessive engine heat and devices are provided for sensing these parameters and controlling the flow of fuel to the engine. In a typical system as shown in the patent, the master control valve includes an oil pressure responsive piston which serves to hold the fuel valve open so long as sufficient oil pressure exists in the engine. The downstream side of the pressurized oil system supplied to the piston is routed in a parallel connection to a heat valve and a coolant loss valve. Both of the valves remain in a closed condition to prevent dumping of the oil under pressure to the sump of the system, which maintains the master control valve in an open position. The master control valve will be closed upon loss of oil pressure, either due to a failure in the engine itself or due to the opening of the coolant loss valve or the heat sensor valve, under predetermined excess or loss conditions.
In coolant loss valves of this type a metal or elastomeric diaphragm is used for responsiveness to coolant pressure to provide linear motion to a valving element which then controls fluid flow, such as oil under pressure, through a main valve orifice. Normally, the valve is closed by coolant pressure and spring means are used to bias the valving element to a normally open position so that upon loss of coolant pressure, the valve will be opened and the fluid at the main valve routed to the sump. In the above-noted patent the actual valve element is an elastomeric disc which is resiliently biased by means of a separate spring to accommodate variable positioning, tolerance variations and the like. Since the coolant loss valve usually operates in a closed condition under coolant pressure it is necessary that the valve operate consistently and repeatedly in this situation and under loss of pressure to move to an open position under the spring bias. Any contamination of the valve could prevent proper operation and the failure to move to an open condition when appropriate could be costly and possibly contribute to a dangerous condition. Since the oil under pressure being controlled is usually contaminated to a certain degree, even though filters are used throughout a typical engine system, this problem is accentuated and it is difficult to design a reliable and consistently operable valve. Further, it is necessary to have a valve design which is efficient and functional and yet be relatively inexpensive as the engine systems are subject to close scrutiny and periodic maintenance.
Another form of coolant loss valve known as the Sentinel Model CL-79 has been widely used in the past. This valve uses a square elastomeric diaphragm and spring-loaded disc holder assembly, the latter being a relatively complex structure comprising a molded plastic stem and valve cup having a snap-in elastomeric seal disc and requiring a nylon washer retainer and specially configured elastomeric seal for sealing the stem of the assembly. The stem is slidably supported in an internal bore of the housing but is subject to contamination in spite of the seals and is subject to premature failure. Further, the main valve seat in this unit is a special relatively expensive stainless steel grommet pressed in place during assembly and chosen to avoid contamination buildup at this critical location.